shit is one of the most popular words in the american dictionary....and this dictionary i suppose. Shit is an word that can be

A. a noun (like pooping, poop, etc)
b. an exclamation (in anger, sadness, happiness, or when something goes horribly wrong)
c. when the word "Holy" is placed on front of it it becomes an expression (like in place of oh my god or something)
d. it can express an amount when "load" is placed after. (an extremely large amount or an extremely small amount)
e. and it can explain 'everything' or 'stuff' in a more expressing way

its most commonly used to make a sentence sound more exciting or more interesting that it normally is. for example.

"the neighbors dog just shit on my lawn"
sounds more interesting than
"the neighbors dog pooped on my lawn"